The invention relates to a switch to be used for detecting a rotational direction of a rotating member in a seat belt retractor to be mounted to a vehicle, such as an automobile, and a seat belt retractor using the same.
A seat belt winding device or retractor to be attached to an automobile has such a function that when a passenger takes a seat and pulls out a seat belt and a tongue is fastened to a buckle device, an extra withdrawing portion of the seat belt is absorbed or retracted. In order to provide the function, in a seat belt retractor of the prior art, a single return spring has been used. When a seat belt is put on a passenger""s shoulder, the passenger pulls out the seat belt against an urging force of the return spring and leaves his hand from the seat belt after a tongue is engaged with a buckle, so that an extra withdrawing portion of the seat belt is wound up by a seat belt retractor until the seat belt fits the passenger""s body.
As explained above, in the seat belt retractor, it is required to satisfy the following points at the same time:
(1) the excessively withdrawing portion of the seat belt is positively wound up until the seat belt fits the passenger""s body, or when the passenger does not wear the seat belt, the withdrawn seat belt is positively stored in a storing portion; and
(2) an unnecessary pressing feeling is not given to a breast portion of the passenger in a normal wearing state.
However, in the seat belt retractor using an urging force of the single return spring, there have been such problems that in case a spring having a weak urging force is used to reduce the pressing feeling against the chest portion of the passenger, a winding force when the seat belt is wound up, i.e. at a storing time, becomes weak, so that an operating ability and storing ability are lowered. On the contrary, in case a spring having a strong urging force is used to obtain a sufficient winding force at the time of winding, the pressing feeding against the chest portion of the passenger at the normal wearing time becomes large.
Also, in a conventional seat belt retractor, there have been problems such that since the single return spring is built in, as a withdrawn amount or length of the seat belt is increased, the return spring is wound to thereby increase its urging force, and as the withdrawing amount of the seat belt is increased, the withdrawing force is increased.
As a device to solve the above problems, the present inventors invented a seat belt winding device or retractor for winding a seat belt by combining a return spring and a motor, and filed a patent application as Japanese Patent Application No. 11-10184 (hereinafter referred to as xe2x80x9cformer inventionxe2x80x9d, not prior art). In the seat belt retractor using the motor for winding the seat belt including the winding device of the former invention, generally, it is required that the motor is stopped when a passenger pulls out the seat belt to allow the seat belt to be pulled out with a small force. As a device for providing this mechanism, there has been proposed a device wherein a rotational direction of a shaft of a spool around which the seat belt is wound is detected, and in case the shaft is rotated in a seat-belt withdrawing direction, power supply to the motor is stopped. The device is also employed in the former invention.
FIG. 5 is a schematic view showing a rotational direction detecting switch used in the former invention. A base frame 21 is provided with a spool 22, and a seat belt is wound around the spool 22. When the spool 22 is driven in a winding or retracting direction, the seat belt is wound up. On the contrary, when the seat belt is pulled out manually, the spool 22 is rotated in a direction opposite to the winding direction. A spool shaft input gear directly connected to the spool shaft is provided with a ring-shape groove 23.
The rotational direction detecting switch includes a switch plate 24 and a limit switch 25, and the switch plate 24 is rotated around a rotating pin 26 as a shaft. Both ends of the switch plate 24 are provided with guides 24a, and when the switch plate 24 is rotated for a predetermined region, the guide 24a hits the ring-shape groove 23 to thereby restrict its rotating region, i.e. angle.
The ring-shape groove 23 contacts a circular arc edge 24b of the switch plate 24. A circular arc groove 24c is formed on an inner side along the circular arc edge 24b. Therefore, when the circular arc edge 24b abuts against the ring-shape groove 23, the circular arc edge 24b is slightly bent to thereby provide a pressing force. Thus, the switch plate 24 is rotated without slipping according to the rotation of the ring-shape groove 23.
FIG. 5 shows a state where the switch plate 24 located at an initial position, i.e. two dotted chain lines, has rotated in a counter-clockwise direction according to a rotation in a clockwise direction of the spool 22, i.e. according to the withdrawal of the seat belt. Under the state, a contact arm 24d provided at a tail portion of the switch plate pushes a movable piece to turn on a limit switch 25. Accordingly, the control device detects that the seat belt has been withdrawn.
In the rotating direction detecting switch according to the former invention as described above, the switch plate 24 is integrally molded of a material, such as a resin, having a certain elasticity. However, since a quantity of an elastic deformation of the circular arc edge 24b is small, in case the rotating shaft of the spool is de-centered or biased, a sufficient pressing force can not be obtained, so that the switch plate 24 is not rotated or, conversely, the pressing force is too strong to thereby damage or wear the circular arc edge 24b. Also, there have been problems such that, by the same reason as mentioned above, a tolerance or manufacturing allowable error of the switch plate 24 becomes small, and a high assembling accuracy is required. Further, since a spool shaft input gear having the ring shape groove 23 and the switch plate 24 must be assembled separately, it is not easy to assemble the rotating direction detecting switch.
In view of the problems, the present invention has been made, and an object of the invention is to provide a rotational direction detecting switch, wherein even if a relative positional accuracy between a rotating member, a rotating direction of which is detected, and the switch plate is not so accurate, a relative positional relationship can be detected.
Another object of the present invention is to provide a rotational direction detecting switch as stated above, wherein an assembling can be easily carried out.
A further other object of the present invention is to provide a seat belt retractor, wherein the rotational direction detecting switch as stated above is employed.
Further objects and advantages of the invention will be apparent from the following description of the invention.
To attain the above objects, according to a first aspect of the invention, there is provided a rotational direction detecting switch including a spring member elastically contacting an outer circumference of a rotating member; a switch plate for supporting the spring member arranged to rotate around a supporting point and having members for restricting a rotating angle thereof; and a switch for detecting a rotational position of the switch plate.
In the rotational direction detecting switch, the spring member supported by the switch plate elastically contacts the outer circumference of the rotating member to thereby generate an elastic force, so that a friction force is generated between the rotating member and the spring member. Thus, the spring member is moved by the friction force according to rotation of the rotating member, and the switch plate supporting the spring member is rotated around the supporting point. The rotation of the switch plate is detected by the switch, such as a limit switch and a proximity switch, to thereby detect the rotational direction thereof. Incidentally, since the switch plate is provided with the members for restricting its rotating angle, the rotation of the switch plate is limited within a predetermined region.
In the rotational direction detecting switch according to the first aspect, since the spring member is used as a member to contact the rotating member, its possible deformation quantity is large, so that even if a rotating shaft of the rotating member is slightly biased, or relative attaching positions of the rotating member and the switch plate are changed, there is no risk that a sufficient force for rotating the switch plate can not be obtained, and that the spring member and the switch plate are damaged. Incidentally, the members for restricting the rotating angle of the switch plate may be integrally formed with the switch plate.
To attain the above objects, according to a second aspect of the invention, in the rotational direction detecting switch according to the first aspect, the members for restricting the rotating angle are projecting members formed on both sides of a forward edge of the switch plate. The projecting members abut against the rotating member to restrict the rotation of the switch plate. Forward edges of the projecting members are connected by a connecting member to thereby form a loop with the forward edge portion of the switch plate, the projecting members and the connecting member to surround the rotating member.
In the rotational direction detecting switch of the second aspect, when the switch plate is incorporated, the rotating member is inserted into the loop formed by the forward edge portion of the switch plate, the projecting members and the connecting member, and the rotating member and the switch plate are incorporated as a sub-unit. Thus, the rotational direction detecting switch can be easily assembled. Incidentally, the projecting members and the connecting member may be formed integrally.
To attain the above objects, according to a third aspect of the invention, there is provided a seat belt retractor having the rotational direction detecting switch of the first or second aspect.
In the seat belt retractor of the invention, the rotational direction detecting switch according to the first or second aspect is used, the rotational direction of the spool can be positively detected to thereby provide the seat belt rector performing a reliable operation. Also, in case the rotational direction detecting switch according to the second aspect is employed, an assembling work can be easily carried out.